Bug: 任务执行中发送的消息一直排队无法送达，需停止后才能发送 / Messages sent while the agent is busy stay queued forever and are never delivered until the task is stopped #20

问题描述 / Problem

Agent 执行任务期间发送的消息（如评审反馈）一直排队，无法送达，只能停止任务后重新发送。

Messages sent while the agent is executing a task stay queued forever and are never delivered. The only workaround is to stop the task and resend.

复现步骤 / Steps to Reproduce

1. 让 Agent 执行一个较长任务；
2. 执行中发送一条消息（如评审反馈）；
3. 消息一直排队无法送达；
4. 停止后重发才能成功。

期望行为 / Expected

消息应在合适时机自动送达，无需中断任务;排队消息应有送达机制或超时提示。

Messages should be delivered automatically without interrupting the task, or at least show a clear UI notice about the queued status.